1. Field of the Invention
The invention lies in the area of the manufacture of cable-shaped members in tubular sheathings. More particularly, the invention relates to a method for inserting a cable-shaped member into an elongated, tubular sheathing which is wound in, or around, a holder, with the holder being subjected to a periodical movement having a vertical component and a longitudinal component aligned with the longitudinal direction of the wound tube, and a device for carrying out the method.
2. Prior Art
In most cases, cables are preferably installed in tubes, inter alia due to the protective effect of a tube and the option of later replacing the cable in a simple manner. If it is possible to insert the cable into the tube in advance (prefab), such often is cheaper than installation in the field. To have this cost advantage actually apply, there must be a simple method of already inserting a cable into a tube at the time of manufacture. Extrusion of the tube around the cable is a simple method per se, but it is difficult to prevent the cable from sticking to the tube, particularly in the event of a close-fitting tube. At the insertion of a cable into a finished tube, it may be of great advantage to already have the tube in a state, e.g., on a reel, in which it may be delivered after insertion of the cable. Methods for inserting a cable in wound state into a tube are known per se. A type of method makes use here of the entraining effect of a fluid flowing, with a relatively high velocity, along a cable to be entrained in a tube. Known here are the application of a fluid, as described in U.S. Pat. No. 4,332,436, and a gaseous medium, such as compressed air, which is disclosed in GB-A-2157019. In the event of tubes in a wound state, in general only relatively limited insertion lengths are capable of being realized with this method.
A second type of insertion method is disclosed, e.g., in EP-A-0091717 and EP-A-0279006. According to the technique disclosed in said references, a reel around which a tube is wound is subjected, with its axis in vertical position, to a periodical movement in which the tube after each period returns to a same initial position. According to EP-A-0091717, the cable moves through the tube, in this case a bore or a channel in a carrier member such as a ribbon, as a result of the periodical movement and its mass inertia. As periodical movements there are named vibrating movements, possibly in combination with a pulsating or shaking movement. The preferably harmonically vibrating movement has a relatively small angle of inclination with respect to the longitudinal direction of the tube. In EP-A-0279006 a similar technique is described, in which the periodical movement is a helical vibration, i.e., a spiral movement having a small vertical component and a larger longitudinal component in the longitudinal direction of the tube. According to both variants of the insertion technique of the second type, the cable is vibrated forward, as it were, along the curved path of the tube on the reel. In this connection, the longitudinal component of the vibration provides a small propelling force, while at the same time the vertical component provides a short-lived reduction of the friction between the cable and the inner surface of the tube. Said insertion technique has the great advantage that basically it does not depend on the cable or tube length. The vibrations, however, evidently require relatively high frequencies and relatively small amplitudes. In order to achieve that such vibrations are well capable of being transmitted from the reel to the tube, it is required that the tube is wound around the reel in a well-fixed manner, to which purpose there are mentioned special techniques. This is rather laborious in a production environment. An added restriction is that acceptable insertion velocities are evidently obtained only if the tube fits relatively loosely around the cable (diameter ratio of two and over).
In JP-A-06201960, there is disclosed yet another insertion technique, which to a certain extent may be considered a combination of the two types of insertion method described. According to said insertion technique, a cable-shaped member, such as an optical fibre or an electric wire, is inserted by way of a free end of a tube, which tube is wound around two capstan-like holders placed at a distance from one another. In this connection, suction is applied at the other end of the tube, while the curved parts of the tube are vibrated at the holders. The vibrations serve to cause a local reduction of the friction in the curved parts between the inner wall of the tube and the cable. The vibrations are orientated vertically, with the suction effect having to provide the forward force on the cable. Said insertion technique roughly has the drawbacks of both types of insertion technique discussed above.